1. Field of the Invention
The present invention relates to a power converter control device for protecting the semiconductor devices of power converters from damage due to over-currents, and a power converter thereof.
2. Description of the Related Art
Generally, a power converter for supplying a variable frequency power source to a load is one that converts a DC power source to an AC of a specified frequency and supplies that to the load. When the DC power source is not directly obtainable, the design is such that a converter device is provided and the DC power source is obtained from the AC power source.
FIG. 1 is a block diagram of power converter 6 and its control device 7 thereof that drive electric motor 5, which is the load, by converting the power source from 3-phase AC power source 1 to a DC power source by converter 2 and converting that DC power source to an AC power source of a specified frequency by inverter device 4.
In converter device 2, the R phase from 3-phase AC power source 1 is inputted to the node between semiconductor device 2U and semiconductor device 2X, the S phase to the node between semiconductor device 2V and semiconductor device 2Y, and the T phase to the node between semiconductor device 2W and semiconductor device 2Z, respectively, and the 3-phase AC is converted to DC. The DC converted by converter device 2 is outputted to the P bus-line (the positive side bus-line) and the N bus-line (the negative side bus-line), is smoothed by smoothing capacitor 3 connected between this P bus-line and N bus-line, and is inputted to inverter device 4.
In inverter device 4, the DC converted by converter device 2 is inputted from the P bus-line and the N bus-line. The design is such that a U phase is outputted from the node between semiconductor device 4U and semiconductor device 4X, a V phase from the node between semiconductor device 4V and semiconductor device 4Y, and a W phase from the node between semiconductor device 4W and semiconductor device 4Z, respectively, and these are outputted to electric motor 5, which is the load.
There are cases of single composition in which each of semiconductor devices 2Uxcx9c2Z and 4Uxcx9c4Z is composed of one semiconductor device, and cases of parallel-connection composition in which each is composed by the parallel connection of multiple semiconductor devices.
With this type of power converter 6, power converter control device 7 is provided for exercising control of power converter 6. Power converter control device 7 is provided with gate driving unit 8 that drives the gates of the semiconductor devices in power converter 6, abnormality detection unit 9 that detects any exceeding of a specified value by the currents flowing in the semiconductor devices of power converter 6 and outputs an abnormality signal, and control unit 10 that controls power converter 6 by sending gate signals to gate driving unit 8. It is designed to detect abnormalities in the semiconductor devices or load short-circuits as abnormality signals, and to take protective action.
However, with a power converter 6 that uses, for example, IGBT (Insulated Gate Bipolar Transistors) as the semiconductor devices, the semiconductor devices have low resistance to short circuits. Therefore, if a DC short-circuit occurs, even if the protective action operates, the detection time will not meet the requirements, and there will be cases when damage occurs to the semiconductor devices.
Here, an IGBT is a static induction self turn-off device and has characteristics that are intermediate between those of a transistor and a thyristor in that, while exhibiting a low constant-current characteristic approaching that of a transistor in the low gate voltage range, when the gate voltage becomes higher, it exhibits a voltage drop approaching that of a thyristor. This IGBT has a safe operation domain in which it may normally operate safely provided the collector current is restricted. However, in a case such as, for example, the occurrence of a load short-circuit, it becomes unstable to operate in the safe operation domain, a large collector current flows, and damage may occur to the semiconductor device.
When an over-current flows in a semiconductor device (IGBT), abnormality detection unit 9 detects that fact, and a gate breaking action is performed by control unit 10 via gate driving unit 8. However, time is consumed from abnormality detection to gate breaking and, particularly in the case of the semiconductor devices being IGBT, there is a risk that the devices will be damaged in the time until gate breaking is executed.
Accordingly, one object of the present invention is to provide a novel power converter control device that may perform its protective action correctly and prevent device damage, even if an abnormality occurs in which a large current flows in the semiconductor devices.
In order to achieve the above object, the present invention has the following composition. That is to say, in a power converter control device provided with:
a gate driving unit that drives the gates of the semi-conductor devices of the power converter;
an abnormality detection unit that detects the fact that the current flowing in the semiconductor device of this power converter has exceeded a specified value, and outputs an abnormality signal;
a control unit that controls the power converter by sending gate signals to the above-mentioned gate driving unit,
xe2x80x83the present invention is a power converter control device in which the above-mentioned gate driving unit is provided with:
a gate constriction means that constricts the semi-conductor device gates when an abnormality signal is inputted from the above-mentioned abnormality detection unit; and
a gate breaking output means that outputs a gate breaking signal to stop the above-mentioned power converter.
Also, in order to achieve the above object, the present invention has the following composition. That is to say, in a power converter control device provided with:
a gate driving unit that drives the gates of the semi-conductor devices of the power converter;
an abnormality detection unit that detects the fact that the current flowing in the semiconductor device of this power converter has exceeded a specified value, and outputs an abnormality signal;
a control unit that controls the power converter by sending gate signals to the above-mentioned gate driving unit,
xe2x80x83the present invention is a power converter control device in which the above-mentioned gate driving unit is provided with:
a gate constriction means that constricts the semi-conductor device gates when an abnormality signal is inputted from the above-mentioned abnormality detection unit;
a gate breaking output means that outputs a gate breaking signal to stop the above-mentioned power converter; and
a gate ON means that maintains the gate signal of any semiconductor device that has become abnormal in the ON state, and turns OFF the gate signals of the semi-conductor devices after the current of the semi-conductor devices has become less than a specified value.